The ever-increasing demand for high-density information storage calls for new approaches for storage of information. The ability to store information in molecular structures provides perhaps the ultimate in data storage density.
The design and synthesis of redox-active molecules for surface attachment provides the foundation for the fabrication of information storage devices that function on the basis of stored charge (see, e.g., Roth et al. (2000) J. Vac. Sci. Technol. B, 18: 2359-2364; Liu et al. (2003) Science, 302: 1543-1545; U.S. Pat. Nos. 6,777,516, 6,728,129, 6,674,121, 6,657,884, 6,451,942, 6,381,169, 6,324,091, 6,272,038, 6,212,093, 6,208,553; PCT Publications WO 02/077633, WO 03/052835, WO 03/038886, etc.). Such surface-attached redox-active molecules can also be used in the fabrication of numerous other devices including, but not limited to solar cells (see, e.g., U.S. Pat. Nos. 6,407,330 and 6,420,648, U.S. Patent Publication 20040244831 A1, and the like). A key feature for the commercialization of redox-based molecular information storage is that each memory cell stores sufficient charge for reliable readout. Similarly a key feature for the commercialization of solar cells is that each cell produce adequate power. Both advantages can be achieved by increasing the packing density of redox-active molecules or molecular subunits on a particular substrate.
An attractive strategy for achieving increased charge density (redox-active unit packing) is to use the vertical dimension. In various embodiments, this can utilize a dyad, triad, or multad of charge storage molecules or subunits. One method for constructing the device would be to attach a pre-synthesized oligomer to the electroactive surface. In this approach, however, it is possible that the oligomers may aggregate and/or may not undergo facile self assembly.
An alternative approach is to grow the oligomer in a stepwise fashion. Such an assembly process, however, has heretofore required the use of protecting groups. The monomeric building blocks were prepared with at least one protecting group, and after each coupling reaction, the protecting group was removed. Thus, one cycle of coupling required three reactions: protecting group introduction, coupling, and protecting group removal. A further limitation stems from the difficulty, in many instances, of identifying suitable conditions for protecting group removal that are compatible with the protected molecules, the components in the molecular architecture under assembly, and the underlying substrate.